Progress in Crystal Growth and Characterization of Materials最新文献

Epitaxial semiconductor quantum dots have been, in the last 40 years or so, at the center of the research effort of a large community. The focus being on “semiconductor physics and devices”, in view of the broad applications and potential, e.g., for efficient temperature insensitive lasers at telecom wavelengths, or as “artificial atoms” for quantum information processing. Our manuscript aims at addressing, with an historical perspective, the specifics of (III-V) epitaxial quantum dot early developments (largely for light emitting) and subsequent years. We will not only highlight the variety of epitaxial structures and methods, but also, intentionally glancing a didactic approach, discuss aspects that are, in general, little acknowledged or debated in the present literature. The analyses will also naturally bring us to examine some of current challenges, in a field which, despite sensational achievements, is, remarkably, still far from being mature in its developments and applications.

Magnesium borate (Mg₂B₂O₅) whiskers are highly regarded as a promising inorganic reinforcing material due to their availability, ease of preparation, and remarkable reinforcing effect. The main objective of this article is to examine the properties of Mg₂B₂O₅ whiskers and to encourage researchers to utilize them, thereby enhancing the characteristics of various composites in a cost–effective manner. Six production methods of Mg₂B₂O₅ whiskers are addressed, and based on these methods, different growth mechanisms of Mg₂B₂O₅ whiskers, including liquid–solid, solid–liquid–solid, vapor–solid, and vapor–liquid–solid mechanisms, are analyzed and summarized. As reinforcing materials, Mg₂B₂O₅ whiskers are widely employed in alloys and polymers, effectively enhancing the physical and chemical properties of the resulting whisker–reinforced composites, including mechanical, friction and wear resistance, and flame retardancy properties. Furthermore, the impact of surface modification of Mg₂B₂O₅ whiskers on the properties of composites was explored. The cost–effectiveness, favorable properties, and wide availability of Mg₂B₂O₅ whiskers make them excellent potential materials for numerous applications, and the article provides an analysis and forecasts the future development direction and prospects of Mg₂B₂O₅ whiskers.

In this review article, we focus on the synthesis process and properties of Fe-Si-B-based soft magnetic alloys that exhibit superior magnetic properties. The process parameters related to the synthesis and characterization of these types of alloys are studied widely and investigated the properties observed in nanocrystalline Cu and Nb-dopped Fe-Si-B-based magnetic alloys. The properties of these materials are an exceptional combination of high permeability, high Curie temperature, low core losses and anisotropy energy, and near zero effective magnetostriction suitable for various applications such as magnetic field sensors, sensors for non-destructive evaluation of materials, motors, transformer cores, electric vehicles, etc. A significant number of research works have been conducted so far and more research is continued to improve their properties in various ways including engineering of materials composition, optimization of synthesis processes, and parameters for easy integration into modern devices. This review article aims to demonstrate a comparison study of the properties of Fe-Si-B- based soft magnetic alloys and to provide the latest updates on their developments toward tailoring the extrinsic (coercivity, and permeability) and intrinsic (Curie temperature and saturation magnetization) properties for conquering the subsequent area of applications.

Under alkaline conditions, silica forms self-assembled mineral compounds which are similar in morphology, nanostructure, and texture to the hybrid biomineral structures that, millions of years ago gave to life. In this review we propose that, during the earliest history of this planet, there was a geochemical scenario that led to large-scale production of both simple and complex organic compounds, many of which were important for prebiotic chemistry. The production was based on a high concentration of silica and high pH. Two main factors affected this process: a) a source of simple carbon molecules that were either synthesized abiotically from reactions associated with serpentinization, or carried by meteorites and produced by their impact on Earth, and b) the formation of self-organized silica-metal mineral compounds that catalyzed the condensation of single molecules in a reduced methane-rich atmosphere. We discuss the plausibility of this geochemical scenario and its catalytic properties and the transition towards a slightly alkaline to Neutral Ocean.

Step pattern stability of the vicinal surfaces during growth was analyzed using various surface kinetics models. It was shown that standard analysis of the vicinal surfaces provides no indication on the possible step coalescence and therefore could not be used to elucidate macrostep creation during growth. A scenario of the instability, leading go macrostep creation, was based on the dynamics of the step train, i.e. the step structure consisting of the high (train) and low (inter-train) density of the steps. The critical is step motion at the rear of the train which potentially leads to the step coalescence i.e. creation of the double and multiple step. The result of the analysis shows that the decisive factor for the step coalescence is the step density ratio in and out of the train. The ratio lower than 2 prevents double step formation irrespective of the kinetics. For higher ratio the coalesce depends on step kinetics: fast incorporation from lower terrace stabilizes the single steps, fast incorporation from upper leads to step coalescence. The double step is slower than the single steps, so the single steps behind catch up creating multistep and finally macrostep structure. The final surface structure consists of the macrosteps and superterraces, i.e. relatively flat vicinal segments. The macrostep alimentation from lower superterrace leads to emission of the single steps which move forward. Thus the single step motion is dominant crystal growth mode in the presence of the macrosteps. These steps finally are absorbed by the next macrostep. The absorption and emission of single steps sustain the macrostep existence, i.e. the macrostep fate is determined the single step dynamics. The condition for single step emission was derived. In addition, the macrosteps are prone to creation of the overhangs which results from surface dynamics coupling to impingement from the mother phase. The angular preferential access of the bulk material to the macrostep edge, leads to the overhang instability and creation of inclusions and dislocations.

This article highlights the electrodeposition of metals, in crystalline or amorphous form, that are monentous in the present era of science and technology. Available literature related to nucleation and growth of metal crystals has been reviewed to gain insight into the mechanism and kinetics. The progress made in the electrodeposition technique, using an ionic liquid (IL) medium, has been detailed for selected metals using different ILs for achieving the controlled growth mechanism driven by electrochemical potential. Theoretical models for nucleation and growth of crystals by electrodeposition have been explained and the effect of crystallization overpotential on the growth of crystal growth has been discussed. Finally, the factors affecting the growth process and the mechanism have been identified and critically analyzed based on the available literature, fundamental knowledge-base, chemistry of ILs, and electrodeposition.

This review article aims to clarify a mechanism of point defects formation in a CZ Si crystal through an experimental arrangement using the two kinds of heat shields with different slow-pulling periods. Point defects in a melt grown silicon crystal have been studied for a long time. The author and his co-researchers have reported about “Mechanism for generating interstitial atoms by thermal stress during silicon crystal growth” [in Progress in Crystal Growth and Characterization of Materials, 66 (2019) 36-46]. The experimental arrangement includes constant growing, changing pulling rate and finally detaching crystals from the melt. The two types of heat shields were used to change the cooling history of the grown crystals, for changing a temperature gradient at a bulk part in the grown crystal, G_b. In order to prove that the formation of an interstitial region or a boundary of vacancies (Vs)/interstitials (Is) in a silicon crystal is a phenomenon of relaxing thermal stress, the author explains that a G_b in a crystal forms thermal stress and causes some silicon atoms at lattice positions to move to the closest interstitial sites to relax the stress. The author defines a new term of metastable interstitial atom, I’, or I's as the plural of I’. The I’ coexists with the metastable vacancy V’ from where the I’ is displaced. The plural of V’ is defined to be V's. The author defines the above state to be a complex (I’+ V’), or (I ’+ V’)s as the plural of (I’+ V’), and explains that the (I’+ V’) s convert to Is and form the Is region. The (I’+ V’) is considered as the Frenkel pair-like complex.

The crystals were firstly pulled with a high pulling rate, and the pulling rate was consequently decreased to a slow one. Then the crystals were pulled with the slow constant pulling rate for different periods making different cooling processes. Finally, the grown crystals were detached from the melt and cooled rapidly. Characterization of defects, such as Vs, Is, and defect-free (D-F) regions were identified in X-ray topographs (XAOP(s)). Wafer lifetime mapping (WLTM(s)) allows confirming dislocation loop (DL) regions. The results show that the Is are generated depending on the pulling period of the slow pulling and the shapes of the heat shields. The Is and DL regions are formed in a region at temperatures near the melting point. The Is form an Is region through a defect-free (D-F) region, forming the Vs/Is boundary. When the thermal stress weakens, the DL region changes to the Is region; the Is region changes to the D-F region; and the D-F region changes to the Vs region. Temperature gradient distribution is induced toward various directions at different parts of the growing crystal depending on the different slow-pulling periods. The temperature gradient, G_b, includes a temperature gradient from the cooled region shaded